Tumblr founder David Karp says that he didn't expect to sell his company to Yahoo, or sell it at all, this year. He says he was motivated to sell because Yahoo would give Tumblr a "shortcut" to "all the very hard things" Tumblr had to learn in order to grow.

But on Thursday Yahoo revealed another pretty good carrot to get Karp to sell: Yahoo will pay him $81 million in cash and stocks if he stays with the company for four years. So it said in a form filed to the SEC, and spotted by AllThingsD's Peter Kafka.

Specifically, he gets Yahoo common stock valued at $41 million and $40 million cash. It averages out to $27.5 million a year.

The filing also says he gets unvested stock options and restricted stock units valued at $29 million. However, a Yahoo spokesperson tells us that goes to Tumblr employees.